(i) Field of the Invention
The present invention relates generally to a movable bridge, and more particularly to a movable built-up bridge structure for use in the road repairing services.
(ii) Description of the Prior Art
Road repair work generally causes traffic jam or even a complete obstacle for traffic and transportation on a road. In an attempt to cope with such undesired conditions, there has been proposed a movable bridge structure of built-up type which is temporarily installed upon a portion of the road, to be repaired, so that the traffic may be maintained without interruption while the road repair work desired is being continued under such bridge structure.
Conventional movable bridges of this type are, as typically shown in FIGS. 22 and 23, of such a general construction which comprises a central bridge portion (a) equipped with a travelling unit having a working space therein, and a ramp portion (b) either of a hinged type or of a sliding type which may be stored somehow into the central portion for the removal and transportation purposes.
According to the conventional constrution of this type bridge structure, there is a physical restriction such that the slope of a ramp cannot be made too large in order for vehicles to pass smoothly thereover. This type of bridge would require a relatively long extension of the entire bridge structure and the bridge structure cannot be designed with a desired short extension. Bridges of the type have a small height, which creates an inconvenience and difficulty in the repair work under the bridge structure.
Accordingly, it is inevitable in the conventional design of such a movable bridge structure that the whole extension of the central bridge portion (a) would exceed, to a considerable extent, the general length allowed for on-road traffic vehicles which would result in an impracticability of use. On the other hand, if the joint section with the ramp portion (b) is designed to be of a hinged type, and when this is adapted in installation on a road having a certain gradient in the transversal direction, it is inevitable in the operation of this bridge structure that there would occur an undesired torsion or twisting load upon the hinged portion which would eventually result in a weak spot in the structural strength.
Also, it is to be noted that construction of a movable bridge of the type stated above is rather complicated resulting in expensive production costs.